1. Field of the Invention
This invention relates to a converting process for the extraction of heavy non-ferrous metals from their ores and to apparatus.
It has preferred reference to the continuous converting of copper, nickel, cobalt or lead sulfides.
2. Description of the Prior Art
The continuous smelting and converting of sulfide minerals to matte or metal is an old concept well known in the art. As long ago as 1898, Garretson in U.S. Pat. No. 596,992 disclosed a three zone smelting, converting and slag settling procedure. He teaches a method for the continuous production of non-ferrous metals from their sulfide ores comprising the steps of continuous smelting of the sulfides in a fuel burning furnace with a long narrow slightly sloped bottom; the resulting matte flows continuously to one or more separate, but communicating, converters in series at one end of the furnace; there the matte is progressively and continuously blown to metal which is withdrawn; the resulting rich slag flows back continuously -- countercurrently to the matte -- through the smelting furnace, is impoverished by contact with the low grade matte therein, flows into a separate but communicating, slag settling zone at the other end of the furnace, and is there subjected to the heating and reducing action of charcoal; matte settles out and flows back to the furnace; and the cleaned slag is discharged.
The concept of the autogenous production of copper matte from sulfide minerals was disclosed in 1915 by Klepinger et al in U.S. Pat. No. 1,164,653. He teaches the spraying of dry, finely divided copper sulfide concentrates with preheated air into a reverberatory-type furnace. The concept of slag cleaning by the washing and reducing action of iron sulfide was disclosed by Stout in U.S. Pat. Nos. 1,416,262 (1922) and 1,544,048 (1925). He teaches progressive cleaning of molten copper-containing slags by their agitation and thorough mixing with pyrite, low grade matte or iron, followed by slag settling under quiescent conditions. Gronningsaeter disclosed in U.S. Pat. No. 2,426,607 (1947) apparatus for reacting slags to recover metals from them by subjecting the slags to reduction and mixing by injection of fuel and air through tuyeres into the body of the slags.
The concept of an elongated, slightly inclined, rotary furnace sufficiently long to provide substantially separate, continuous metal melting and refining zones was disclosed by Sherwood in 1970 in U.S. Pat. No. 3,542,350. Much information pertinent to non-ferrous pyrometallurgy is furnished in many of the Reports of Investigation of the U.S. Bureau of Mines, e.g., "Autogenous Smelting of Copper Sulfide Concentrate", R. I. 7705 (1973).
One of the present applicants disclosed in 1954, U.S. Pat. No. 2,668,107, autogenous smelting of copper and nickel sulfide concentrates by injecting dry sulfides with tonnage oxygen and flux into an impermeably encased chamber. Matte or metal and slag are continuously produced, the matte or metal is discharged from one end of the furnace, and the slag is discharged from the other end. The rich slag from the high grade matte end of the furnace is depleted of its metal values by employing the principle of countercurrent flow of matte or metal relative to the slag. If desired, after passage over a raised hearth barrier to separate the slag and matte layers, and, in any event, prior to discharge from the furnace, the slag is given a final cleaning by washing it with a shower of molten, low grade matte droplets rich in iron sulfide. Furnace off-gas contains a high concentration of sulfur dioxide. He also disclosed in 1961, U.S. Pat. No. 3,004,846 and in subsequent U.S. Pat. Nos. 3,030,201; 3,069,254; 3,468,629; 3,516,818; 3,615,361 and 3,615,362 the conversion of copper, nickel and lead sulfide materials to metal, in appropriately operated top-blown rotary oxygen converters. He teaches top blowing techniques using downwardly directed gas lances to impinge process gases of controlled analysis onto or through the surface of the bath at controlled temperatures. He also teaches the need for "a sufficiently high degree of agitation to provide efficient and effective gas-solid-liquid contact throughout the bath, which is conducive to efficient elimination of iron, sulfur and impurities" and he emphasizes "the extreme importance and necessity connected with strong induced turbulence of the furnace bath". Application of his turbulent bath principle "enhances heat transfer, increases the overall rate of the chemical reactions, minimizes compositional gradients within each phase and significantly reduces diffusion barriers between the slag and the sulfide phase".
In a 1950 publication "A Survey of the Thermodynamics of Copper Smelting" (Transactions AIME, Volume 188) one of the present applicants presented an analysis of the physical chemistry involved in the smelting and converting of mixtures of copper and iron sulfides to produce crude metal and waste slag. A major teaching is that "the chemical activities of oxygen and sulfur are two of the most important thermodynamic yardsticks to be applied to copper smelting processes". The publication also includes quantitative demonstrations that the production of crude metal and waste slag from sulfide concentrate should be regarded as a process of "progressive and controlled oxidation" in a "sequence of steps". Thermodynamic calculations provide numerical estimates of the oxygen and sulfur activities which prevail in conventional copper smelting, converting and fire refining operations. The publication discloses that the matte-slag systems characteristic of these operations are subject to "tremendous variation in oxygen pressure", as much as 10.sup.6 -fold. He teaches that these variations can be related to the practical problems of controlling matte and slag stoichiometry, operating temperatures, magnetite formation and slag losses. His subsequent publications disclose oxygen and sulfur activities in mattes and slags over the wide ranges of composition and temperature encountered in the smelting and converting of copper- and iron-containing sulfides.
During the past several years a number of skilled and forward-looking investigators have proposed a variety of ways and means for solving the serious problems connected with pyrometallurgical transformation of sulfide concentrates to metal in a continuous process. These include Worner, U.S. Pat. No. 3,326,671 (1967), Themelis et al, U.S. Pat. No. 3,542,352 (1970), Maelzer et al, U.S. Pat. No. 3,687,656 (1972), and Morisaki et al of Mitsubishi Metal Corporation. Despite their efforts none have satisfactorily overcome all of the crucial obstacles involved. In the first of these patents, operating complications and limitations are imposed by the three zone concept in the type of apparatus employed and by the reliance on top blowing techniques using downwardly directed gas lances. The second procedure utilizes concurrent flow of matte and slag. The white metal blowing section -- where high oxygen and low iron sulfide activities are essential -- is contiguous to the slag reducing section -- where low oxygen and high iron sulfide activities are essential. The process has some of the restrictions characterizing current industrial operations because of the similarity of the apparatus employed to a conventional Pierce-Smith converter. The third patent describes a semi-continuous series of intricate operations in a multi-compartment apparatus, which include top blowing techniques using downwardly directed gas lances. The fourth procedure employs three separate, but communicating, individual furnaces for continuous smelting, converting and slag cleaning; it also relies on top blowing techniques using downwardly directed gas lances. This process retains several disadvantages of the established art.